JP2844965B2 - Vehicle rear wheel steering system - Google Patents

Abstract

PURPOSE:To prevent vehicle behavior from becoming unstable due to multiplier effect of lack of slip restraint of wheels in a traction control device and reversed-phase steering of rear wheels against front wheels. CONSTITUTION:An AWS microcomputer 65 detects vehicle travel conditions by receiving detected signals normally from a front wheel steering angle sensor 61, a vehicle speed sensor 62, and a yaw rate sensor 63, and steers and control rear wheels RW1 and RW2 in phase and in reversed phase against front wheels FW1 and FW2, in accordance with the detected vehicle travel conditions. On the other hand, a TRC microcomputer 70 normally performs tractive action which restrains wheels slip, but if this tractive action is not selected by a driver, or not preformed due to malfunction, or causes a large allowable wheel slip rate due to tractive action the AWS microcomputer 65 prohibits the above mentioned reversed-phase steering of the rear wheels RM1 and RW2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear wheel steering device for a vehicle, and more particularly to a rear wheel steering device for a vehicle equipped with a traction control device for suppressing wheel slip.

[0002]

2. Description of the Related Art Conventionally, a traveling state of a vehicle such as a steering state of a front wheel, a traveling speed of a vehicle, a state of a traveling road surface, etc. is detected, and a steering amount of a rear wheel is determined according to the detected traveling state. Rear wheel steering devices that steer a rear wheel in phase and in a reverse phase with respect to a front wheel are well known. (For example, Japanese Patent Laid-Open No. 2-2
No. 62471)

[0003]

However, the above-mentioned conventional rear-wheel steering system detects traction of a wheel and controls driving force, braking force and the like on the wheel when the slip is detected to avoid traction of the wheel. When applied to a vehicle equipped with a control device, the traction function in the traction control device is not selected, the traction function is not operating due to a failure of the traction control device, or the allowable slip ratio of the traction control device is large. Therefore, when the rear wheels are largely steered in the opposite phase with respect to the front wheels, the stability of the vehicle is not regarded as important. May become unstable. The present invention has been made to address the above-described problem, and an object of the present invention is to limit the amount of reverse-phase steering of the rear wheels with respect to the front wheels in accordance with the degree of suppression of wheel slip by the traction control device, so that the behavior of the vehicle is constantly controlled. It is an object of the present invention to provide a rear wheel steering device for a vehicle that is kept stable.

[0004]

In order to achieve the above-mentioned object, the structural features of the invention described in claim 1 are as follows.
As shown in the figure, a slip suppression means 1a for detecting a wheel slip and suppressing the slip, and a slip suppression means 1
a) is applied to a vehicle equipped with a traction control device 1 comprising a selection means 1b for selecting operation or non-operation of the rear wheel steering mechanism 2 for steering the rear wheels, and a rear wheel for controlling the rear wheel steering mechanism 2 And a steering control means 3 for steering the vehicle to a steering amount according to the traveling state of the vehicle.
When the non-operation of the slip suppressing means 1a is selected by the selecting means 1b, a steering restricting means 4 for controlling the steering control means 3 to prohibit reverse-phase steering of the front wheels of the rear wheels is provided.

As shown in FIG. 1, the structural features of the invention according to claim 2 are: a slip suppression means 1a for detecting a wheel slip and suppressing the slip; Fail detection means 1 for detecting abnormality
c, a rear wheel steering mechanism 2 that steers the rear wheels, and a rear wheel steering mechanism 2 that controls the rear wheels to adjust the rear wheels to a steering amount according to the traveling state of the vehicle. In a rear-wheel steering device having a steering control means 3 for steering, when the failure detection means 1c detects an abnormality of the traction control apparatus 1, the steering control means 3 is controlled to perform reverse-phase steering of the rear wheels with respect to the front wheels. Is provided in the steering limiting means 4 for prohibiting.

Further, as shown in FIG. 1, a structural feature of the invention according to claim 3 is that the traction control device 1 detects a wheel slip and suppresses a wheel slip rate to a target value or less. The vehicle includes a rear wheel steering mechanism 2 that is applied to a mounted vehicle and steers rear wheels, and a steering control unit 3 that controls the rear wheel steering mechanism 2 to steer the rear wheels to a steering amount according to a traveling state of the vehicle. In the rear wheel steering device of the vehicle, the steering control means 3 is controlled in accordance with the target value of the slip ratio by the traction control device 1 so that when the target value is large, the steering amount of the rear wheel with respect to the front wheel in the reverse phase direction is reduced. The steering limiting means 4 for limiting the steering amount is provided.

[0007]

According to the first aspect of the present invention, if the operation of the slip suppression means 1a is selected by the selection means 1b, the slip of the wheels is suppressed by the slip suppression means 1a. In this case, the steering control means 3 controls the rear wheel steering mechanism 2 to freely steer the rear wheels. On the other hand, if the non-operation of the slip suppressing means 1a is selected by the selecting means 1b, the slip of the wheels is not suppressed, but in this case, the steering limiting means 4
Restricts the steering control of the rear wheels by the steering control means 3 to prohibit the reverse steering of the rear wheels to the front wheels.

As a result, according to the first aspect of the present invention, the rear wheels are steered in the opposite phase to the front wheels in a state where the wheels are slipping due to the non-operation of the slip suppressing means 1a. Since the unstable element of the behavior is not superimposed, the running stability of the vehicle is improved.

According to the second aspect of the present invention, if the slip suppressing means 1a is normal, the slip of the wheels is properly suppressed by the slip suppressing means 1a. Means 3 controls the rear wheel steering mechanism 2 to freely steer the rear wheels. On the other hand, in a state where an abnormality has occurred in the slip suppressing means 1a and the slip of the wheels is not properly suppressed, the abnormality is detected by the fail detecting means 1c, and the steering limiting means 4 controls the steering of the rear wheels by the steering control means 3. And prohibit the reverse-phase steering of the front wheels of the rear wheels.

As a result, according to the second aspect of the invention, the vehicle in which the rear wheels are steered in the opposite phase to the front wheels in a state where the slip of the wheels is not properly suppressed due to the abnormality of the slip suppression means 1a. Therefore, the running stability of the vehicle is improved.

Further, in the invention according to claim 3 configured as described above, the traction control device 1 suppresses the wheel slip rate to a target value or less. On the other hand, in the rear wheel steering device, the steering limiting means 4 controls the steering control means 3 according to the target value of the slip ratio, and when the target value is large, the steering control means 3 and the rear wheel steering mechanism 2 The reverse steering amount of the rear wheels is limited to a small steering amount. As a result, when the wheel slip rate is suppressed to a small value,
The rear wheel has a possibility of being largely steered in the opposite phase with respect to the front wheel, and when there is a possibility that the slip ratio of the wheel may increase, the reverse phase steering amount of the rear wheel is kept small.

As a result, according to the third aspect of the present invention, the rear wheel is not largely steered in the opposite phase to the front wheel at the same time as the slip ratio of the wheel is increased, and the behavior of the vehicle is unstable. Since the elements are not superimposed, the running stability of the vehicle is improved.

[0013]

The embodiments of the present invention will be described below in order. a. First Embodiment First, a first embodiment will be described with reference to the drawings. FIG. 2 schematically shows a front and rear wheel steering device of a vehicle according to the first embodiment. The front and rear wheel steering devices are composed of left and right front wheels FW1, F
Front wheel steering mechanism A for steering W2, and left and right rear wheels RW1, R
A rear wheel steering mechanism B that steers W2 in conjunction with the steering of the left and right front wheels FW1 and FW2 and the like, and a rear wheel steering electrical control circuit C that electrically controls the rear wheel steering mechanism B.

The front wheel steering mechanism A has a rack bar 11 that is displaced in the axial direction and steers the left and right front wheels FW1 and FW2.
The rack bar 11 is connected to a steering wheel 14 via a pinion gear 12 and a steering shaft 13, and is slidably connected to left and right tie rods 16a, 16b connected to rack ends 15a, 15b fixed to both ends thereof.
Left and right front wheels FW1, FW2 are connected via left and right knuckle arms 17a, 17b rotatably connected to 6a, 16b. A control valve 18 composed of a four-way valve is mounted in the middle of the steering shaft 13. The valve 18 is connected to a conduit P from the hydraulic pump 21 in accordance with the steering torque acting on the steering shaft 13.
1 is supplied to one oil chamber of the power cylinder 22 and the hydraulic oil in the other oil chamber of the cylinder 22 is discharged to the reservoir 23 via the conduit P2. The power cylinder 22 drives the rack bar 11 in the axial direction according to the supply and discharge of hydraulic oil, and the left and right front wheels FW1, FW
Assists the steering of W2. The hydraulic pump 21 is driven by the engine 24.

The rear wheel steering mechanism B has a relay rod 31 which is displaced in the axial direction to steer the left and right rear wheels RW1, RW2. The relay rod 31 is a housing 3 supported by the vehicle body.
2 is supported so as to be displaceable in the axial direction, and the left and right rear wheels RW1 and RW2 are connected at both ends thereof via left and right tie rods 33a and 33b and left and right knuckle arms 34a and 34b as in the case of the front wheel steering mechanism A. Connected. A power cylinder 35 for driving the relay rod 31 in the axial direction is formed in the housing 32. The power cylinder 35 is formed of a left and right oil chamber 35b liquid-tightly partitioned by a piston 35a fixed to the relay rod 31. , 35c. In the left and right oil chambers 35b, 35c, preloaded springs 36a, 36b are incorporated so as to penetrate the relay rod 31.
6b urges the relay rod 31 to the neutral position.

A power cylinder 3 is provided in the housing 32.
5, a spool valve 42 constituting a hydraulic copying mechanism is incorporated. The spool valve 42 includes a valve sleeve 42a housed in the housing 32 in a liquid-tight and slidable manner in the axial direction, and a valve spool 42b housed in the sleeve 42a and having one end fixed to the housing 32. When the sleeve 42a is displaced leftward with respect to the spool 42b, the hydraulic pump 4
3 is supplied to the supply port 42c via the conduit P3 and supplied to the power cylinder 3 via the inflow / outflow port 42d.
5 to the left oil chamber 35b.
The hydraulic oil in the right oil chamber 35c is discharged to the reservoir 23 through the inflow / outflow port 42e, the discharge port 42f, and the conduit P4. Therefore, at this time, the relay rod 31 is displaced rightward, and the left and right rear wheels RW1, RW2 are steered leftward.

When the valve sleeve 42a is displaced rightward with respect to the valve spool 42b, the hydraulic oil supplied from the hydraulic pump 43 to the supply port 42c via the conduit P3 is supplied to the power cylinder via the inflow / outflow port 42e. 35 to the right oil chamber 35c.
The hydraulic oil in the left oil chamber 35b is discharged to the reservoir 23 through the inflow / outflow port 42d, the discharge port 42f, and the conduit P4. Therefore, in this case, the relay rod 31 is displaced leftward, and the left and right rear wheels RW1, RW2 are steered rightward. The hydraulic pump 43 is also driven by the engine 24.

A lever 45 is inserted through a through hole 42a1 provided at the right end of the valve sleeve 42a.
Numeral 5 is fitted on the inner peripheral surface of the through hole 42a1 so as to be tiltable and slidable on the outer peripheral surface of the spherical nodal ridge provided at the intermediate portion. The lower end of the lever 45 is a piston 35a.
The lever 45 is rotatably and vertically slidably fitted in an annular groove 35a1 provided on the outer periphery of the lever 45. The upper end of the lever 45 is rotatably connected to the center of the pin 46.

The right end of the pin 46 is slidably inserted into the hole 32a formed in the housing 32 in the axial direction thereof, and the left end of the pin 46 is formed on the nut member 47 by a male screw formed on the outer periphery. It is screwed on the screw. A male screw is formed on the outer periphery of the nut member 47, and the member 47 is screwed by this male screw to a female screw formed on the inner periphery of a hole 32 b provided in the housing 32. In such a case, the pitch or screw direction of the screw portion connecting the pin 46 and the nut member 47 and the screw portion connecting the nut member 47 and the housing 32 are different from each other. The pin 46 is displaced in the axial direction. The nut member 47 is driven by a step motor 48, and rotates according to the rotation of the motor 48. Here, the step motor 48 can be rotated by a predetermined pulse signal in a forward / reverse direction by a desired number of rotations.
The rotation shaft 8 is connected to the nut member 47 so as to be slidable in the axial direction and fixed in the rotation direction. The step motor 48 rotates in a positive direction and a negative direction as described later. When the step motor 48 rotates in the positive (or negative) direction, the pin 46 is displaced in the right (or left) direction on the drawing. I do. Also, the pin 46 is right (or left)
When the lever 45 is displaced in the direction, the upper end of the lever 45 rotatably attached to the center of the pin 46 is also displaced in the right (or left) direction, and the upper end of the lever 45 is provided at the center of the lever 45 by the outer peripheral surface of the nodal protrusion. The valve sleeve 42a is displaced in the right (or left) direction. If the valve sleeve 42a is displaced right (or left), the relay rod 31 is displaced left (or right) as described above, and the left and right rear wheels RW1, RW2 are steered right (or left) and the piston is moved. In order to displace the lower end of the lever 45 in the left (or right) direction by 35a,
The valve sleeve 42a is displaced in the left (or right) direction, and the displacement with the valve spool 42b is eliminated.

The rear wheel steering electric control circuit C includes a front wheel steering angle sensor 61, a vehicle speed sensor 62, a yaw rate sensor 63, and a motor rotation angle sensor 64. The front wheel steering angle sensor 61 detects the rotation angle of the steering shaft 13 or the axial displacement of the rack bar 11, and outputs a detection signal representing the steering angle δH of the left and right front wheels FW1, FW2. The vehicle speed sensor 62 detects a vehicle speed V that changes in proportion to the rotation speed by, for example, measuring the rotation speed of the output shaft of the transmission.
Is output. The yaw rate sensor 63 is
The yaw rate γ is detected by measuring the rotational angular velocity of the vehicle body around the vertical, and a detection signal representing the yaw rate γ is output. The motor rotation angle sensor 64 includes the step motor 4
The rotation angle δθ of the rotation member fixed coaxially with respect to the rotation axis 8 is detected, and a detection signal representing the rotation angle δθ is output.

Here, if the sign of the detection signal or the like is matched in the actual direction for the sake of easy understanding, the front wheel steering angle δH
Is a positive (or negative) value when the steering wheel 14 is rotated in the right turning (or left turning) direction, and the yaw rate γ
Is positive (or negative) when the vehicle turns right (or left)
When the step motor 48 rotates in the positive (or negative) direction, the pin 46 is displaced in the right (or left) direction, and at that time, the rotation angle δθ becomes a positive (or negative) value.

These sensors 61 to 64 are provided by a rear wheel steering microcomputer (hereinafter referred to as an AWS microcomputer) 65.
The AWS microcomputer 65 is connected to a bus 65.
a, respectively, the ROM 65b, the CPU 65c,
It comprises a RAM 65d and an I / O 65e (input / output interface). The ROM 65b stores programs corresponding to the flowcharts of FIGS.
c sequentially accesses the ROM 65b from the closing to the opening of an ignition switch (not shown) to execute the program. In addition, the ROM 65b includes
, The front wheel steering angle proportional coefficient Kδ corresponding to the vehicle speed V
As shown in FIG. 7, a yaw rate proportional coefficient Kr with respect to the vehicle speed V is stored in the form of a table. That is, a front wheel steering angle proportional coefficient read address and a yaw rate proportional coefficient read address are generated from the vehicle speed V,
When the ROM 65b is accessed with both address data, the front wheel steering angle proportional coefficient Kδ and the yaw rate proportional coefficient Kr corresponding to the vehicle speed V are read out as data. RAM65
d is a storage area for temporarily storing variables and the like required when the CPU 65c executes the program.
The PU 65c sequentially stores the RAM 65d via the bus 65a.
To access.

The I / O 65e is connected to the respective sensors 61 to 64 and the drive circuit 66, and the respective sensors 61 to 6
4, and outputs a drive signal Δr for controlling the rotation angle of the step motor 48 to the drive circuit 66. That is, the CPU 65c
Inputs the detection data of each of the sensors 61 to 64 via the I / O 65e as appropriate when executing the program,
The drive signal △ r calculated by the processing described later is output to the I / O6
Output to the drive circuit 66 via 5e. Drive circuit 66
Supplies a drive pulse corresponding to the drive signal Δr supplied from the AWS microcomputer 65 to the step motor 48, thereby rotating the step motor 48 by an angle corresponding to the drive signal Δr. Is controlled to maintain the position after rotation.

Further, a traction control microcomputer (hereinafter referred to as a TRC microcomputer) 70 is connected to the I / O 65e, and exchanges control signals with the TRC microcomputer 70.

The TRC microcomputer 70 performs traction control for suppressing wheel spin caused by excessive driving force during starting acceleration on a road surface having a small friction coefficient.
As shown in FIG. 8, the main part of the traction control electric control circuit D is configured to control the throttle opening in the engine intake mechanism E. TRC microcomputer 70
Are ROMs 70b, C connected to the bus 70a, respectively.
It comprises a PU 70c, a RAM 70d, and an I / O 70e (input / output interface).

The ROM 70b stores a program shown in FIG. 9 executed by the CPU 70c, and stores a throttle opening degree having a predetermined relationship with the engine rotational speed shown in FIG. 10 in a table.
Is a storage area for temporarily storing variables and the like necessary for executing the program. In addition, the I / O 70e
Include first and second driven wheel rotational speed sensors 71a, 71a.
1b, a drive wheel rotational speed sensor 72, an engine rotational speed sensor 73, an air flow meter 74, a throttle opening sensor 75, a throttle motor 76, and a switch 77 are connected.

First and second driven wheel rotational speed sensors 71
a, 71b detect the rotational speeds θfl, θfr of the left and right front wheels FW1, FW2 as driven wheels, and detect the rotational speeds θfl, θfr.
A detection signal representing fr is output. The drive wheel rotational speed sensor 72 indirectly detects the rotational speeds θr of the left and right rear wheels RW1 and RW2 based on the rotational speed of the output shaft of the transmission 80, and outputs a detection signal representing the rotational speed θr. The engine rotational speed sensor 73 detects the rotational speed NE of the engine 81 and outputs a detection signal indicating the rotational speed NE.
The air flow meter 74 measures the amount of intake air by the engine 81 and outputs a detection signal indicating the amount of intake air. The throttle opening sensor 75 detects the opening θM of the first throttle 82 driven by the accelerator operation by the driver, and outputs a detection signal representing the opening θM. The throttle motor 76 is to fully open the second throttle 83 in a normal state and to close appropriately during the acceleration slip control. The throttle motor 76 is controlled by a drive signal θTR so that the second throttle 83 has an opening represented by the drive signal θTR. Open and close. Note that both the drive signal θTR and the detection signal θM are values representing the degree of opening of each of the throttles 83 and 82 as a percentage of the degree of opening when fully opened. The switch 77 is for instructing whether or not to operate the traction control. The switch signal is set to a high level when the operation is instructed and to a low level when the non-operation is instructed.
Output SW.

Next, the operation of the embodiment configured as described above will be described. In the rear wheel steering electric control circuit C, CP
U65c is closed when the ignition switch is closed.
Start the execution of the programs shown in FIGS.
Processing of main routine consisting of 0 to 114 and step 2
The processing of the subroutine consisting of 00 to 220 and steps 300 to 302 is repeatedly executed, and the left and right rear wheels RW
1 and RW2.

After performing initial settings such as clearing variables in step 100, the CPU 65c sets in step 10
In step 2, a subroutine for calculating a target rotation angle δθ * of the step motor 48 is executed. In this subroutine, first, in step 200, the running state of the vehicle is detected. That is, the CPU 65c controls the front wheel steering angle sensor 61, the vehicle speed sensor 62, and the yaw rate sensor 6 via the I / O 65e.
3 receives data representing the detected front wheel steering angle δH, vehicle speed V, and yaw rate γ, and temporarily stores the data in the RAM 65d.

Next, in step 210, the CPU 65c accesses the ROM 65b to obtain the front wheel steering angle proportional coefficient Kδ and the yaw rate proportional coefficient Kr corresponding to the vehicle speed V stored in the RAM 65d. As described above, R
The OM 65b is used not only as a storage area of a program but also as a data table. Therefore, for each data of the front wheel steering angle proportional coefficient Kδ and the yaw rate proportional coefficient Kr, the data representing the detected vehicle speed V is processed in a predetermined procedure to be the address data of the ROM 65b, which is stored in the address indicated by the address data. Read the value.

In steps 200 and 210, the left and right rear wheels RW
When the processing for obtaining the various factors that determine the steering amount of the RW1 and RW2 is completed, a target rotation angle δθ * with respect to the step motor 48 is obtained in step 220 according to the following equation (1).

## EQU1 ## δθ * = Kδ · δH + Kr · γ Front wheel steering angle proportional coefficient Kδ read out corresponding to vehicle speed V
As shown in FIG. 6, at the time of the vehicle speed “0”, the maximum value becomes a negative value, and gradually approaches “0” as the vehicle speed increases. As shown in FIG. 7, the yaw rate proportional coefficient Kr is "0" up to a constant vehicle speed, and becomes a constant positive value at a vehicle speed that is gradually increased when the vehicle speed exceeds the same constant vehicle speed.

After calculating the target rotation angle δθ *, the CPU 6
5c determines in step 104 whether the switch 77 in the traction control electric control circuit D is turned on. In this case, the switch 77 is connected to the I / O 70e of the TRC microcomputer 70, and the CPU 65c switches the switch 77 via the I / O 65e and the I / O 70e.
, And determines whether or not the switch 77 is turned on. Now, the driver judges the road condition and thinks that traction control is necessary,
If the switch 77 is turned on, the CPU 65
c sets "1" to a flag TRCFLG for traction control control in steps 104 and 106.

Next, the CPU 65c performs a rear wheel steering process at step 108. In the rear wheel steering process, the CPU 6
5c is a motor rotation angle sensor 6 in step 300 of FIG.
4 inputs the detected motor rotation angle δθ,
In step 2, a signal representing the difference δθ * −δθ between the calculated target rotation angle δθ * and the current motor rotation angle δθ is output to the drive circuit 66 as a drive signal Δr for the step motor 48. Then, the drive circuit 66 rotates the step motor 48 by the angle represented by the drive signal Δr, and maintains the position after the rotation.

When the drive signal Δr is output, the drive circuit 66
Outputs a drive pulse to the step motor 48, and the step motor 48 rotates to the target rotation angle δθ * according to the drive pulse. If the target rotation angle δθ * is negative (or positive), 48 rotates to a rotation position in a negative direction (or a positive direction). At this time, since the pin 46 is displaced leftward (or rightward) from the reference position, the upper portion of the lever 45 rotatably attached to the intermediate portion also displaces leftward (or rightward). The lever 45 is attached to the valve sleeve 4 by the outer peripheral surface of a spherical nodal ridge provided in the middle.
The valve sleeve 42a is also displaced to the left (or right) side because it is fitted in the through hole 42a1 provided at the right end of the 2a, and the supply port 4 is connected to the supply port 4 via the conduit P3 from the hydraulic pump 43.
The hydraulic oil supplied to 2c flows into the left oil chamber 35b (or right oil chamber 35c) via the inflow / outflow port 42d (or inflow / outflow port 42e), and displaces the piston 35a in the right (or left) direction. With the right oil chamber 35c (or the left oil chamber 3
The hydraulic oil in 5b) is discharged from the inflow / outflow port 42e (or the inflow / outflow port 42d) to the reservoir 23 via the conduit P4.

Since the piston 35a is fitted in the groove 35a1 with the lower end of the lever 45, when the piston 35a is displaced right (or left) by hydraulic oil, the lower end of the lever 45 is moved right (or left). (Or left), and the lever 45 returns the valve sleeve 42a to the right (or left). Therefore, when the piston 35a is displaced right (or left) by a certain amount, the hydraulic oil is not supplied to the left oil chamber 35b (or the right oil chamber 35c), and the piston 35a stops. As the piston 35a is displaced, the relay rod 31 is also displaced in the right (or left) direction, and the knuckle arms 34a, 34b are connected via the tie rods 33a, 33b.
34b is rotated counterclockwise (or clockwise) around its rotation axis, and the left and right rear wheels RW1 and RW2 are steered left (or right).

As a result of the steering of the left and right rear wheels RW1 and RW2, the driver operates the steering wheel 14 to steer the right and left front wheels FW1 and FW2 to the right (or left) while the vehicle is running at low speed. In this case, the front wheel steering angle δH input in step 200 becomes a positive (or negative) value, and the yaw rate γ also becomes a positive (or negative) value. The angle proportional coefficient Kδ has a large negative absolute value and the yaw rate proportional coefficient Kr has a value of “0” or a small positive value. Therefore, the target rotation angle δθ * calculated in step 220 is a negative (or positive) value. Therefore, the left and right rear wheels RW1, RW2
Is steered to the left (or right), that is, the left and right front wheels FW
1 and FW2, the vehicle is steered in the opposite phase, and the small turning performance of the vehicle running at low speed is improved.

On the other hand, if the vehicle is running at high speed and the driver operates the steering wheel 14 to steer the left and right front wheels FW1 and FW2 to the right (or left), as in the above case, the process proceeds to step 200. The input front wheel steering angle δH has a positive (or negative) value and the yaw rate γ has a positive (or negative) value. However, the front wheel steering angle proportional coefficient Kδ set in step 210 becomes “0” or a negative value with a small absolute value, and the yaw rate proportional coefficient Kr becomes a positive value with a large absolute value. Is a positive (or negative) value. Therefore, the left and right rear wheels RW1, RW2 are steered in the right (or left) direction, that is, steered in the same phase as the left and right front wheels FW1, FW2, and the running stability of the vehicle during high-speed running is improved.

On the other hand, when the driver turns off the switch 77 considering that traction control is unnecessary, the CPU 6
5c determines "NO" in step 104, and sets a traction flag TRCFLG to "0" in step 110 to control the traction control to be deactivated.

Next, at step 112, the CPU 65c determines whether or not the left and right rear wheels RW1, RW2 are to be steered in the opposite phase to the left and right front wheels FW1, FW2. In this case, if the front wheel steering angle δH is positive, the left and right front wheels FW1,
If FW2 is steered to the right and negative, it indicates steering to the left, whereas if the target rotation angle δθ * is positive, the left and right rear wheels RW1, RW2 are steered to the right and negative. If there is, the steering is performed to the left. Therefore, whether or not the steering should be performed in the opposite phase may be determined, for example, by determining whether or not the product of the multiplication of the front wheel steering angle δH and the target rotation angle δθ * becomes negative.

If the vehicle is running at low speed and the left and right rear wheels RW1, RW2 are to be steered in the opposite phase to the left and right front wheels FW1, FW2, the CPU 65c determines "YES" in step 112. In step 114, the target rotation angle δθ * is set to “0” to perform rear wheel steering. That is, the step motor 48 is not driven to the calculated target rotation angle δθ *, but is forcibly returned to the neutral position. Also, when the vehicle is running at high speed, the left and right rear wheels RW1, RW
If No. 2 is to be steered in-phase with the left and right front wheels FW1 and FW2, the CPU 65c determines “NO” in step 112, and sets the left and right rear wheels RW1 and RW2 to the left and right front wheels by the above-described processing in step. Steering is performed in phase with respect to FW1 and FW2. As a result, when the switch 77 is turned off, that is, when the traction flag TRCFLG is “0”, only the steering of the left and right rear wheels RW1 and RW2 in the in-phase direction with respect to the left and right front wheels FW1 and FW2 is allowed, and the opposite phase direction is allowed. Steering is prohibited.

During the rear wheel steering control by the CPU 65c, in the TRC microcomputer 70, the CPU 70c repeatedly executes the program consisting of steps 400 to 422 corresponding to the flowchart of FIG. I do.

In this program, the CPU 70c first detects in step 400 whether or not an acceleration slip has occurred. Many methods are already known for detecting the acceleration slip, but in this embodiment, the left and right front wheels FW1, FW detected by the driven wheel rotational speed sensors 71a, 71b.
2 is calculated, and the difference between the average speed and the rotation speed θr of the drive wheel detected by the drive wheel rotation speed sensor 72 is calculated. Is calculated, and when the ratio becomes a predetermined ratio or more, it is determined that the acceleration slip has occurred. If the same ratio is calculated and it is determined that no acceleration slip has occurred, a control signal θTR representing an opening of “100%” is sent to the servo motor 76 at step 422 so that the second throttle 83 is fully opened. Then, the process of calculating the same ratio and making the same judgment again is repeated.

However, due to the low coefficient of friction of the road surface and the high acceleration, the left and right rear wheels RW as drive wheels are used.
When the acceleration slip occurs in RW1 and RW2, the CPU 70c determines "YES" in step 400, and proceeds to step 40.
At 2, it is determined whether or not the traction flag TRCFLG is "1". Since the traction flag TRCFLG is stored in the AWS microcomputer 65, the CPU 70c sets the I / O 7
0e and the value of the flag TRCFLG via the I / O 65e, and only when the flag TRCFLG is set to "1", "YES" is determined in the step 402 and the steps 404 to 420 are performed. Is executed. If the traction flag TRCFLG is “0”, the CPU 65c determines “NO” in step 402 and executes the processing in step 422, so that the acceleration slip suppression processing is not executed.

In the acceleration slip suppression processing, the CPU 70c
Determines in step 404 whether or not the acceleration slip suppression process has been executed for the first time. In this case, a flag FFLG indicating whether or not the execution has been performed for the first time (“0” indicates that it is not the first time, and “1” indicates that it is the first time) is prepared.
Is set to “1”, and if it is determined in step 404 that this is the first time, the flag FFLG is set to “0”.
Thus, when the acceleration slip suppression processing is not executed, "1" indicating that the flag FFLG is the first time is set, and when the execution of the acceleration slip suppression processing is started, the flag is not the first time. "0" must be set.

Since this is the first time, the CPU 70c inputs the rotational speed NE of the engine 80 detected by the engine rotational speed sensor 73 in step 406, and
In step 08, the throttle opening .theta.T, which is 85% of the torque corresponding to the rotational speed NE, is read from the table stored in the ROM 70b.

Next, at step 410, the CPU 70c detects the first throttle 8 detected by the throttle opening sensor 75.
2, the throttle opening .theta.T read out at step 412 is compared with the opening .theta.M of the first throttle 82, and at step 414 or 416, the smaller one is applied to the servo motor 76. Set to drive signal θTR. This is to set the initial value of the second throttle 83 at the start of the acceleration slip suppression process, and to set the initial value smaller than the opening of the first throttle 82 operated by the driver, The driving force is reduced from the start of the acceleration slip suppression processing. If the initial value is too large, the driving force does not decrease at the start of the acceleration slip suppression process, so that a time lag occurs.If the initial value is too small, the driving force decreases too quickly, and the riding comfort deteriorates. The throttle opening is set to an initial value so as to be 85% of the set torque.

After the initial value of the throttle opening is set,
In step 418, the CPU 70c outputs a drive signal θTR representing the same initial value to the servomotor 76. This allows
The servo motor 76 closes the second throttle 83 up to the opening represented by the drive signal θTR, and the drive force decreases to a torque ratio of 85% or less. When the drive signal θTR is output, it is determined again whether or not an acceleration slip has occurred in step 400, and if the acceleration slip has occurred and the flag TR
If CFLG is "1", it is determined in step 404 whether the acceleration slip suppression processing is the first time.

It is determined that this is not the first time,
In step 420, the CPU 70c performs feedback control to increase or decrease the opening of the second throttle so as to have an opening corresponding to the acceleration slip, thereby suppressing the acceleration slip. Thereafter, this process is repeated until the acceleration slip is no longer detected.
In step 422, the PU 70c controls the control signal θ representing the opening degree of “100%” so as to fully open the second throttle 83.
TR is output to the servomotor 76.

When this is observed over time, as shown in FIG. 11, after the acceleration slip is detected at time T1, the second throttle 83 is detected at time T2.
Is closed to the initial value θTR, and thereafter, the opening of the second throttle 83 is increased or decreased so as to suppress the acceleration slip. When the acceleration slip disappears at time T3, the second throttle 83 is closed at time T4. Return the opening to 100%. Therefore, the slip ratio of the left and right rear wheels RW1, RW2 as drive wheels is suppressed to a predetermined value.

As described above, according to the first embodiment,
The driver considers that traction control is unnecessary, and in a state where the switch 77 is set to off and the acceleration slip of the left and right rear wheels RW1 and RW2 as the driving wheels is not suppressed, steps 104 and 110 to 114 in FIG. By processing, the left and right front wheels FW of the left and right rear wheels RW1, RW2
Since the anti-phase steering of the FW1 and FW2 is prohibited, the vehicle behavior is prevented from becoming unstable due to the lack of suppression of the acceleration slip and the synergistic effect of the anti-phase steering of the left and right rear wheels RW1 and RW2. In cases other than the above, since steering control from the opposite phase of the left and right rear wheels RW1 and RW2 to the same phase is permitted, the steering function of the rear wheels RW1 and RW2 is sufficiently exhibited, and the stability of the vehicle is improved. Is good.

B. Second Embodiment Next, a second embodiment of the present invention will be described. The hardware configuration of this embodiment is the same as that of the first embodiment, and the ROM 65b of the AWS microcomputer 65 stores the program corresponding to the flowchart of FIG.
The second embodiment differs from the first embodiment in that a program corresponding to the flowchart of FIG. In the flowchart of FIG. 12, the same parts as those in the first embodiment are denoted by the same reference numerals.

In the second embodiment configured as described above, the CPU 65c executes the processing in step 112 of FIG.
Is "YES", that is, it is determined that the left and right rear wheels RW1 and RW2 should be steered in the opposite phase to the left and right front wheels FW1 and FW2.
A detection signal indicating the vehicle speed V from the vehicle is input, and the vehicle speed V and a predetermined vehicle speed V0 (for example, 10 km / h)
Is determined whether the vehicle is traveling at or below the predetermined vehicle speed V0 (slightly low speed).

If the vehicle is running at a very low speed, the above-described steps 104 and 1 are performed even if the switch 77 is turned off because the driver does not need traction control.
After the processing of steps 10 and 112, the CPU 65c proceeds to step 120.
Is determined to be "YES" at step 108, and at step 108, the rotational position of the step motor 48 is set to the target rotation angle δθ * calculated by the processing at step 102 described above. In this case, since the vehicle speed V is extremely low (10 km / h or less), the target rotation angle δθ * is determined by connecting the left and right rear wheels RW1 and RW2 to the left and right front wheels FW.
1 and FW2 are set to values that largely steer in the opposite phase to the rear wheels RW1 and RW2.
2 is largely steered in the opposite phase.

On the other hand, if the vehicle is not in a very low speed state and the driver 77 considers that traction control is unnecessary and the switch 77 is turned off, the CPU 65c determines "NO" in step 120 and proceeds to step 11 described above.
By the processing of No. 4, the left and right rear wheels RW1, RW2 are maintained in the neutral state.

As described above, by turning the left and right rear wheels RW1 and RW2 in opposite phases, if the vehicle is in a very low speed state, the small turning performance of the vehicle is exhibited regardless of the traction control. If the vehicle is running at a very low speed as described above, the behavior of the vehicle does not become unstable even if the left and right rear wheels RW1 and RW2 as drive wheels accelerate and slip. In other cases, as in the first embodiment, when the switch 77 is turned off and the acceleration slip of the left and right rear wheels RW1 and RW2 as drive wheels is not suppressed, the left and right rear wheels RW1 and RW2 Left and right front wheels FW1, FW
2, the vehicle is prevented from becoming unstable due to the lack of suppression of the acceleration slip and the synergistic effect of the left and right rear wheels RW1, RW2 due to the reverse phase steering.

C. Third Embodiment Next, a third embodiment of the present invention will be described. The hardware configuration in this embodiment is the same as that of the AWS microcomputer 65.
This is the same as the first embodiment except that the friction coefficient sensor 67 is connected to the I / O 65e. In terms of software, the program corresponding to the flowchart of FIG. 13 is stored in the ROM 65b of the AWS microcomputer 65 instead of the program corresponding to the flowchart of FIG. This embodiment differs from the first embodiment in that a program corresponding to the flowchart of FIG. 14 is stored instead of a program corresponding to the flowchart. In the flowcharts of FIGS. 13 and 14, the same parts as those in the first embodiment are denoted by the same reference numerals.

The friction coefficient sensor 67 detects the friction coefficient μ between the running road surface and the tire. Specifically, the friction coefficient sensor 67 determines whether the road surface is wet due to rain or the temperature is low and the road surface is frozen. The friction coefficient value μ is estimated based on various factors such as whether an anti-skid brake system (not shown) frequently operates, whether the reaction force to the steering wheel operation is large, or the motion state of the vehicle, and detects the estimation result. Output as a signal.

In the third embodiment configured as described above, after the determination of "YES" in step 400 of FIG. 14, the CPU 70c of the TRC microcomputer 70 executes step 4
At 30, the presence or absence of an abnormality in the traction control electric control circuit D is detected. Specifically, the driven wheel rotational speed sensor 7 in the traction control electric control circuit D
1a, 71b, a drive wheel rotational speed sensor 72, an engine rotational speed sensor 73, an air flow meter 74, a throttle opening sensor 75, a throttle motor 76, a switch 77, and the presence or absence of any abnormality in the TRC microcomputer 70 itself are detected.

If no abnormality has occurred in the traction control electric control circuit D, the CPU 70c operates as shown in FIG.
In step 430 of No. 4, “NO” is determined, and the program proceeds to step 402, so that the traction control electric circuit D operates in the same manner as in the first embodiment.

At this time, in the AWS man-con 65, the target rotation angle δθ * in step 102 of FIG.
Is calculated, the CPU 65c determines in step 130 whether or not a fail flag FAILFLG indicating the state of the traction control electric control circuit D is "1". The fail flag FAILFLG is set to the TRC microcomputer 70.
And I / O7 of TRC microcomputer 70
0e, which is initially set to "0" and is set to the traction control electric control circuit D
Is set to "1" by the process of step 432 in FIG. In this case, since no abnormality has occurred in the traction control electric control circuit D, the CPU 65c returns “NO” in step 130.
That is, it is determined that the fail flag FAILFLG is "0", and the program proceeds to step 104 and the subsequent steps.
Steering control of the left and right rear wheels RW1, RW2 is performed in substantially the same manner as in the embodiment.

However, in this case, if the switch 77 is off and the left and right rear wheels RW1, RW2 are to be steered in opposite phases, steps 104, 110, 11 are performed.
After the process of 2, the CPU 65c inputs a signal from the friction coefficient sensor 67 in step 132 and determines whether or not the friction coefficient μ is small. If the vehicle is traveling on a slippery road surface and the friction coefficient μ is small, the CPU 65c determines “YES” in this step 132, and maintains the left and right rear wheels RW1, RW2 in the neutral state by the processing of step 114. . Therefore, when the switch 77 is turned off and traction control is not performed and the vehicle is traveling on a slippery road surface, the left and right rear wheels RW1 and RW2 are steered in the opposite phases to the left and right front wheels FW1 and FW2. And the vehicle behavior does not become unstable due to the synergistic effect of the acceleration slip of the left and right rear wheels RW1 and RW2 as the driving wheels and the above-mentioned reverse-phase steering.

Even when the traction control is not performed because the switch 77 is turned off, if the road surface is hard to slip, that is, if the friction coefficient μ is large, the CPU
65c determines “NO” in step 132 and executes the process of step 108. In this case, the left and right rear wheels RW1 and RW2 are also steered in the opposite phases with respect to the left and right front wheels FW1 and FW2. The small turning performance of the vehicle is improved.

On the other hand, when an abnormality occurs in the traction control electric control circuit D, the CP of the TRC microcomputer 70
U70c determines "YES" in step 430 of FIG. 14, and sets fail flag FAILFLG and traction flag TRCFLG to "1" and "0" respectively in step 432. Then, the CPU 70c always determines "NO" based on the traction flag TRCFLG set to "0" in step 402, and controls the second throttle 83 to a fully open state in step 422. Accordingly, in this case, the traction control by the traction control electric control circuit D is not performed.

At this time, in the rear wheel steering electric control circuit C, the CPU 65c determines "YE" based on the fail flag FAILFLG set to "1" in step 130.
S ”, and the program proceeds to step 112 and subsequent steps. In this case, the left and right rear wheels RW1 and RW2 are
Only when the steering is to be performed in the opposite phase to W1 and FW2 and the friction coefficient μ is small, the CPU 65c determines “YES” in both steps 112 and 132, and in step 114, the left and right rear wheels RW1. , RW2 are maintained in a neutral state. As a result, if the traction control is not performed due to the abnormality of the traction control electric control circuit D and the running surface is in a slippery state, the right and left rear wheels RW1 and RW2 are steered in the opposite phases to the left and right front wheels FW1 and FW2. Is prohibited, the behavior of the vehicle is prevented from becoming unstable due to the synergistic effect of the acceleration slip of the left and right rear wheels RW1 and RW2 as the drive wheels and the above-described reverse-phase steering.

Even if the traction control is not performed due to the abnormality of the traction control electric control circuit D, if the road surface is hard to slip and the friction coefficient μ is large, the CPU 65c determines “NO” in step 132. Then, at step 108, the left and right rear wheels R
W1 and RW2 are controlled to a steering angle corresponding to the target rotation angle δθ * calculated in step 102. As a result, in this case, the left and right rear wheels RW1 and RW2 are steered in the opposite phase to the left and right front wheels FW1 and FW2, and the small turning performance of the vehicle is improved.

D. Fourth Embodiment Next, a fourth embodiment of the present invention will be described. The hardware configuration of this embodiment is the same as that of the first embodiment, and the ROM 65b of the AWS microcomputer 65 stores the program corresponding to the flowchart of FIG.
17 is stored in a table provided in the ROM 65b.
And that the maximum rotation angle .delta..theta _MAX of the step motor 48 of the characteristic shown in the graph is stored in ROM70b the TRC microcomputer 70, instead of the program corresponding to the flowchart of FIG. 9, the program corresponding to the flowchart of FIG. 16 Is stored, and a target slip ratio S * having characteristics shown in the graph of FIG. 18 is stored in a table provided in the ROM 70b. In the flowcharts of FIGS. 15 and 16, the same parts as those in the first embodiment are denoted by the same reference numerals.

In the fourth embodiment configured as described above, the CPU 70c of the TRC microcomputer 70 inputs the control signal SW from the switch 77 at step 440 in FIG. 16 and the traction control is selected by the driver. Is determined.

If the driver has turned on the switch 77, the CPU 70c determines "YES" in step 440, and in step 442, the driven wheel rotational speed sensor 71
a, 71b and the detection signals from the drive wheel rotational speed sensor 72 are input, and the rotational speeds θf of the left and right front wheels FW1, FW2 are input.
Data representing l and θfr is temporarily stored in the RAM 70d. Next, in step 444, the CPU 70c calculates R based on the average value (θfl + θfr) / 2 of the rotation speeds θfl and θfr.
The target slip ratio S * is read from the table in the OM 70b. In this case, the left and right front wheels FW1 and FW2 that are driven wheels
Since the average value (θfl + θfr) / 2 of the rotation speeds of the above indicates the vehicle speed, the target slip ratio S * is set to a large value when the vehicle speed is low, and is set to a small value as the vehicle speed increases. (See FIG. 18). Next, CPU
70c is a left and right rear wheel RW which is a driving wheel in step 446.
1, the slip ratio S of RW2 is calculated based on the following equation (2).

S = (2 · θr−θfl−θfr) / (θfl + θfr)

After the determination of the target slip ratio S * and the calculation of the slip ratio S, the CPU 70c compares the two values S * and S at step 448. In this case, if the slip ratio S is larger than the target slip ratio S *, the CPU 70c makes a “YES” determination in step 448, and performs the same processing in steps 404 to 420 as in the first embodiment to determine whether the left and right driving wheels The acceleration slip of the rear wheels RW1, RW2 is suppressed. If the slip ratio S is equal to or less than the target slip ratio S *, the CPU 70c determines "NO" in step 448, and opens the second throttle 83 fully by the processing in step 422, which is the same as in the first embodiment. The suppression of the acceleration slip is released. As a result of such control, the slip ratio S of the left and right rear wheels RW1 and RW2 becomes substantially equal to the target slip ratio S
* Maintained below.

[0070] Also, if the driver turns off the switch 77, CPU70c is determined to be "NO" in step 440, to set the target slip ratio S * at step 450 to slip maximum value S _MAX, By the process of step 422, the second throttle 83 is fully opened to release the suppression of the acceleration slip. In this case, the slip maximum value S
_MAX corresponds to a value at which the maximum rotation angle δθ _MAX of the step motor 48 becomes “0”, as shown in FIG.

On the other hand, in the rear wheel steering electric control circuit C, the CPU 65c of the AWS microcomputer 65
In step 02, the target rotation angle δθ * of the step motor 48 is calculated based on the above equation 1 in the same manner as in the first embodiment, and in step 140, the left and right rear wheels are calculated in the same manner as in the first embodiment. RW1, RW2 are left and right front wheels FW1, FW2
It is determined whether or not the vehicle is in a state to be steered in the opposite phase. In this case, if the left and right rear wheels RW1 and RW2 are not in a state to be steered in the opposite phase, the CPU 65c determines “NO” in step 140, and determines in step 108 that the case of the first embodiment is different. Similarly, left and right rear wheels RW1,
RW2 is steered according to the target rotation angle δθ *.

If the left and right rear wheels RW1 and RW2 are to be steered in the opposite phase to the left and right front wheels FW1 and FW2, the CPU 65c determines in step 142 the table in the ROM 65b based on the target slip ratio S *. From the maximum rotation angle δθ _MAX of the step motor 48. As shown in FIG. 17, the maximum rotation angle δθ _MAX becomes smaller as the target slip ratio S * becomes larger, and becomes “0” when the target slip ratio S * is larger than the maximum slip value _SMAX .

After determining the maximum rotation angle δθ _MAX , the CPU
65c is the target rotation angle δθ * in steps 144 and 148.
The absolute value of | δθ * | (corresponding to the steering amount of the left and right rear wheels RW1, RW2) is equal to or within the maximum rotation angle .delta..theta _MAX. In this case, if the target rotational angle .delta..theta * is greater than the maximum positive rotation angle δθ _MAX, CPU65c is determines as "YES" in step 144, step 14
In step 6, the target rotation angle δθ * is changed to a value δθ _MAX (positive value). The target rotation angle δθ * is the negative maximum rotation angle −δθ.
If smaller than _MAX , the CPU 65c determines “YES” in step 148, and changes the target rotation angle δθ * to a value −δθ _MAX (negative value) in step 150. Target rotation angle .delta..theta * absolute value | .delta..theta * | is within the range of the maximum rotational angle δθ _MAX, CPU65c step 144,14
In step 8, the determination is "NO", and the program proceeds to step 108 without changing the target rotation angle δθ *.

By the processing of steps 142 to 150, the absolute value | δθ * | of the target rotation angle δθ * is limited to a smaller value as the target slip ratio S * increases. In particular, when traction control is not performed in the traction electric control circuit D, the target slip ratio S * is set to the maximum slip value S.
Since it is set to _MAX , the target rotation angle δθ * is set to “0”.

Then, in step 108, the CPU 65c changes the steering angles of the left and right rear wheels RW1, RW2 to the target rotation angle δ.
Since the steering is performed in accordance with θ *, the more the traction electric control circuit D suppresses the acceleration slip of the left and right rear wheels RW1 and RW2, which are the drive wheels, to a smaller value, the smaller the rear wheels RW1
RW2 is allowed to perform large reverse phase steering. Then, as the suppression of the acceleration slip is eased, the allowable steering amount of the left and right rear wheels RW1, RW2 to the opposite phase is limited to a small value, and when the traction control is not performed,
Steering of the rear wheels RW1, RW2 is prohibited.

As a result, also in the fourth embodiment, the vehicle behavior is prevented from becoming unstable due to the synergistic effect of the acceleration slip of the left and right rear wheels RW1 and RW2 as the driving wheels and the above-mentioned reverse-phase steering. You. Also, according to this embodiment,
Since both the suppression of the acceleration slip and the opposite phase steering of the left and right rear wheels RW1 and RW2 are continuously controlled, the traction control and the rear wheel steering function can be maximized.

E. Modifications of Each of the Above Embodiments In the above second embodiment, when the vehicle is running at a very low speed, even if the switch 77 is turned off and the traction control is not operating, step 1 in FIG.
In the determination process of 20, the prohibition of the reverse-phase steering of the left and right rear wheels RW1, RW2 with respect to the left and right front wheels FW1, FW2 is released. Instead of the determination process of step 120, the third embodiment shown in FIG. When the vehicle is traveling on a road surface having a large friction coefficient μ by performing the comparison determination processing of the magnitude of the friction coefficient μ in step 132, the inhibition of the reverse phase steering of the left and right rear wheels RW1 and RW2 is released. You may do so. Further, the process of step 132 is inserted between the determination process of step 120 and the reverse-phase steering prohibition process of step 114, so that the vehicle is traveling at a very low speed even when the traction control is not operating. In the case and when the vehicle is traveling on a road surface having a large friction coefficient μ, the inhibition of the reverse-phase steering of the left and right rear wheels RW1 and RW2 may be canceled.

In the third embodiment, when the vehicle is traveling on a road surface having a large friction coefficient μ, even if an abnormality has occurred in the traction electric control circuit D and the traction control is not working, Although the prohibition of the reverse-phase steering of the left and right rear wheels RW1 and RW2 with respect to the left and right front wheels FW1 and FW2 is released by the determination processing of step 132 in FIG. 13, instead of the determination processing of step 132, the second embodiment is used. When the vehicle is running at a very low speed, the prohibition of the reverse-phase steering of the left and right rear wheels RW1 and RW2 is released by performing the very low speed running determination process of step 120 in FIG. Is also good. Further, the processing of the step 120 is inserted between the determination processing of the step 132 and the reverse-phase steering inhibition processing of the step 114,
Even when the traction control is not operating, the left and right rear wheels RW1 and RW are provided when the vehicle is traveling on a road surface having a large friction coefficient μ and when the vehicle is traveling at a very low speed.
The second prohibition of reverse phase steering may be canceled.

Also, in the fourth embodiment, as in the second and third embodiments, when the vehicle is traveling at a very low speed and when the vehicle is traveling on a road surface having a high friction coefficient μ. Alternatively, the reverse-phase steering restriction of the left and right rear wheels RW1, RW2 may be released. In this case, the determination processing of step 120 of FIG. 12 and step 132 of FIG.
5 when the vehicle is traveling at a very low speed and when the vehicle is traveling on a high friction coefficient road.
The program may be advanced to step 108 by skipping the process of 0. In other cases, as described above, the processing of step 108 may be performed after the processing of steps 142 to 150.

In the first to fourth embodiments,
The rotational speed difference between the driven wheel and the drive wheel is used to detect the acceleration slip, but the rotational speed of the drive wheel is differentiated to detect the acceleration, and the acceleration slip is detected when the acceleration exceeds a predetermined value. Such as detecting the occurrence of a slip, or calculating the driving force that the drive wheels can effectively transmit to the road surface, and detecting the acceleration slip when the engine output exceeds the driving force. It is also possible to detect by configuration.

Further, in the first to fourth embodiments, the driving force is reduced by opening and closing the throttle opening in order to suppress the acceleration slip. However, the driving force is reduced by operating the brake. For example, it is also possible to suppress the acceleration slip by another configuration.

[Brief description of the drawings]

FIG. 1 is a claim correspondence diagram corresponding to the configuration of each invention described in the claims.

FIG. 2 is a schematic diagram of a vehicle steering device according to each embodiment of the present invention.

FIG. 3 is a flowchart corresponding to a main routine executed by the AWS microcomputer of FIG. 2 according to the first embodiment of the present invention.

FIG. 4 relates to each embodiment of the present invention.
It is a flowchart corresponding to 15 target rotation angle calculation routines.

FIG. 5 according to each embodiment of the present invention;
It is a flowchart corresponding to 15 rear wheel steering routines.

6 is a graph showing a change characteristic of a front wheel steering angle proportional coefficient with respect to a vehicle speed stored in the AWS microcomputer of FIG. 2 according to each embodiment of the present invention.

7 is a graph showing a change characteristic of a yaw rate proportional coefficient with respect to a vehicle speed stored in the AWS microcomputer of FIG. 2 according to each embodiment of the present invention.

FIG. 8 is a schematic diagram of a traction control device of the vehicle shown in FIG. 2 according to each embodiment of the present invention.

FIG. 9 relates to the first and second embodiments of the present invention.
5 is a flowchart corresponding to a control program executed by an RC microcomputer.

FIG. 10 is a diagram showing a table content of an initial opening of a second throttle stored in the TRC microcomputer of FIG. 8 according to each embodiment of the present invention.

FIG. 11 is a time chart showing a time change of the opening degree of the second throttle of FIG. 8 according to each embodiment of the present invention.

FIG. 12 is a flowchart corresponding to a main routine instead of the flowchart of FIG. 3 according to the second embodiment of the present invention.

FIG. 13 is a flowchart corresponding to a main routine instead of the flowchart of FIG. 3 according to the third embodiment of the present invention.

FIG. 14 is a flowchart corresponding to a control program in place of the flowchart of FIG. 9 according to the third embodiment of the present invention.

FIG. 15 is a flowchart corresponding to a main routine in place of the flowchart of FIG. 3 according to the fourth embodiment of the present invention.

FIG. 16 is a flowchart corresponding to a control program in place of the flowchart of FIG. 9 according to the fourth embodiment of the present invention.

FIG. 17 is a graph showing a change characteristic of the maximum rotation angle with respect to a target slip ratio stored in the AWS microcomputer of FIG. 2 according to the fourth embodiment of the present invention.

FIG. 18 is a graph showing a change characteristic of the target slip ratio with respect to the vehicle speed stored in the TRC microcomputer of FIG. 8 according to the fourth embodiment of the present invention.

[Explanation of symbols]

A: front wheel steering mechanism, B: rear wheel steering mechanism, C: rear wheel steering electric control circuit, D: traction control electric control circuit, E: engine intake mechanism, FW1, FW2: front wheels, R
W1, RW2: rear wheels, 14: steering wheel, 61: front wheel steering angle sensor, 62: vehicle speed sensor, 63: yaw rate sensor, 65: AWS microcomputer, 67: friction coefficient sensor,
70: TRC microcomputer; 71a, 71b: driven wheel rotational speed sensor; 72: drive wheel rotational speed sensor; 73: engine rotational speed sensor; 75: throttle opening sensor;
... Servo motor, 77 ... Switch.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B62D 137: 00 (72) Inventor Osamu Takeda 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Hiroaki Tanaka 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Shin Koike 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Mizuho Sugiyama 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Kaoru Ohashi 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Hitoshi Iwata 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) ) Inventor Masaru Ishikawa 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (58) Field surveyed (Int. Cl. ⁶ , DB name) B62D 6/00-6/06 B62D 7/14

Claims (3)

(57) [Claims] The present invention is applied to a vehicle equipped with a traction control device including a slip suppression unit that detects a wheel slip and suppresses the slip, and a selection unit that selects operation or non-operation of the slip suppression unit. A rear wheel steering device for a vehicle, comprising: a rear wheel steering mechanism that steers a rear wheel; and a steering control unit that controls the rear wheel steering mechanism to steer a rear wheel to a steering amount according to a traveling state of the vehicle. A vehicle having a steering limiting means for controlling the steering control means when the non-operation of the slip suppressing means is selected by the selecting means to inhibit reverse-phase steering of the front wheels of the rear wheels. Wheel steering device. 2. The vehicle according to claim 1, wherein the vehicle is equipped with a traction control device including slip suppression means for detecting slip of a wheel and suppressing the slip, and fail detection means for detecting an abnormality of the slip suppression means. A rear wheel steering mechanism for steering the rear wheel steering mechanism; and a steering control means for controlling the rear wheel steering mechanism to steer a rear wheel to a steering amount according to a traveling state of the vehicle. A rear wheel steering device for a vehicle, comprising: a steering limiting device for controlling the steering control device when the abnormality of the traction control device is detected by the detecting device to prohibit reverse-phase steering of a front wheel of a rear wheel. . 3. A rear wheel steering mechanism that is applied to a vehicle equipped with a traction control device that detects wheel slip and suppresses a wheel slip rate to a target value or less, and that steers rear wheels, and the rear wheel steering mechanism. And a steering control means for controlling a rear wheel to a steering amount according to a traveling state of the vehicle by controlling the steering control according to a target value of a slip ratio by the traction control device. A rear wheel steering device for a vehicle, further comprising a steering limiter for controlling a unit to limit a steering amount of the rear wheel in a reverse phase to a front wheel to a small steering amount when the target value is large.